Callitriche terrestris is an annual herb, minute, stems tufted, to 5 cm long (usually much less), bright green, appearing almost moss-like, simple to much-branched, rooting at nodes.
Leaves opposite, to 0.5 cm long, widest above middle.
Flowers barely visable with hand lens, unisexual, one of each sex or separately in each leaf axil, no petals or sepals, ovary 4-lobed, flattened, on a stalk about as long as fruit, stamen single.
Fruit to 0.7 cm, 4-lobed, 1-seed per lobe; April-Sept.
Wetland status: OBL.
Frequency in NYC: Very infrequent.
Habitat: Partially shaded, wet to damp soil.